Exemplary embodiments of the present invention relate to a single frequency synthesizer based frequency division duplex (FDD) transceiver, and more particularly, to a single frequency synthesizer based FDD transceiver which enables frequency up-conversion and frequency down-conversion using a single frequency synthesizer at the time of transmission and reception.
FIG. 1 shows the construction of a common wireless communication transceiver, FIG. 2 shows the construction of the transmitter of a common analog circuit-based direct conversion structure, FIG. 3 shows the construction of the transmitter of a common digital-IF structure, FIG. 4 shows the construction of the receiver of the common analog circuit-based direct conversion structure, and FIG. 5 shows the construction of the receiver of the common digital-IF structure.
In a wireless communication transceiver structure, such as that shown in FIG. 1, when transmission is performed, a digital front-end 111 performs digital signal processing. A transmitter 112 converts the digital output of the digital front-end 111 into analog output, filters an analog baseband signal, performs frequency up-conversion into a radio frequency (RF) band, and then performs power amplification. Next, a duplexer 114 sends the result signal to an antenna 115.
The transmitter 112 may include a direct conversion structure and a digital-intermediate frequency (IF) structure.
The direct conversion structure performs frequency up-conversion into an RF band frequency to be outputted at once.
As shown in FIG. 2, in the transmitter of the analog circuit-based direct conversion structure, digital-analog converters (DACs) 211 and 212 first convert a digital baseband in-phase (I) signal and a digital baseband quadrature (Q) signal into respective analog baseband signals. At this time, generated images are removed by low pass filters 213 and 214.
Mixers 216 and 217 mix the analog baseband signals with respective RF carrier frequencies generated from a frequency synthesizer 215 and perform frequency up-conversion on the I signal and the Q signal. The converted I signal and the converted Q signal are summed. The summed signal is subject to power amplification through a power amplifier (PA) 219 after passing through a bandpass filter 218 and is then transmitted.
In contrast, as shown in FIG. 3, the transmitter of the digital-IF structure performs frequency up-conversion from baseband signals to low IF band signals and then performs frequency up-conversion from the low IF band signals to an RF band signal again.
More particularly, mixers 311 and 312 perform frequency up-conversion from a digital baseband I signal and a digital baseband Q signal into IF band signals in the digital region. The IF band signals are summed. A DAC 314 converts the summed signal into an analog signal. At this time, a generated image is removed by a low pass filter 315.
Here, an IF may be obtained by a numerically controlled oscillator (NCO) 313.
A mixer 317 mixes the analog signal with an RF carrier generated from a frequency synthesizer 316 and performs frequency up-conversion from the mixed signal to an RF band signal. The RF band signal is subject to power amplification through a PA 319 after passing through a bandpass filter 318 and is then transmitted.
The digital-IF structure does not have a problem, such as the leakage of a local oscillator (LO) or a DC offset, as compared with a direct conversion structure.
Meanwhile, in a wireless communication transceiver structure, such as that shown in FIG. 1, when reception is performed, an RF band signal is received through the antenna 115 and the duplexer 114. A receiver 113 performs low-noise signal amplification on the RF band signal, performs frequency down-conversion from the amplified signal to a baseband signal, performs analog signal processing and analog-digital conversion on the baseband signal, and inputs the resulting signal to the digital front-end 111.
Like the transmitter 112, the receiver 113 also has a direct conversion structure and a digital-IF structure.
As shown in FIG. 4, in the receiver of the common analog circuit-based direct conversion structure, frequency down-conversion from an RF band signal to a baseband signal is performed at once.
A low noise amplifier (LNA) 411 amplifies the RF band signal received from the antenna 115 via the duplexer 114 in the state in which low noise remains. Mixers 412 and 413 mix the amplified RF band signal with carriers generated from a frequency synthesizer 416 and perform frequency down-conversion from the mixed signals to baseband signals.
Low pass filters 414 and 415 remove frequency signals that may be aliased from the baseband signals. ADCs 417 and 418 convert the respective analog signals into a digital baseband I signal and a digital baseband Q signal.
In contrast, as shown in FIG. 5, the receiver of the digital-IF structure performs down-conversion into a low IF band signal and then performs frequency down-conversion from the low IF band signal to a baseband signal again.
More particularly, an LNA 511 performs low-noise amplification on a received signal. Mixers 512 and 513 mix the amplified signal with carriers generated from a frequency synthesizer 516 and perform frequency down-conversion from the mixed signals to primary IF band signals. Low pass filters 514 and 515 remove aliasing images from the primary IF band signals. ADCs 517 and 518 convert the analog IF band signals into digital IF band signals. A digital mixer 519 mixes the digital IF band signals and performs frequency down-conversion from the mixed IF band signal into a baseband signal again. Here, the IF may be obtained by an NCO 520.
As described above, the wireless communication transceiver requires two or more PLL (phase locked loop) frequency synthesizers. In the frequency division dual mode of an FDD, a transmitter frequency band and a receiver frequency band are separately set, and a transceiver performs transmission and reception at the same time. Thus, frequency synthesizers are used in a transmitter and a receiver, respectively, in order to vary the transmission frequency and the reception frequency independently.
That is, each of the transmitter and the receiver of the direct conversion structure requires one frequency synthesizer, and the digital-IF structure requires a frequency synthesizer for up-conversion from an IF band signal to an RF band signal and a frequency synthesizer for down-conversion from an RF band signal to an IF band signal.
Furthermore, a superheterodyne structure is also widely used in addition to the direct conversion structure or the digital-IF structure. The superheterodyne structure requires two frequency synthesizers in each of a transmitter and a receiver.
As described above, in the FDD system, the transceiver requires two or more frequency synthesizers because transmission and reception are performed at the same time and the transmitter and the receiver cannot share the frequency synthesizer unlike in a time division duplex (TDD) system. Accordingly, the FDD system is problematic in that the area, power consumption, and design complexity of the entire system are increased.
A related prior art includes U.S. Patent Application Publication No. 2009/0075601, entitled Low-IF Transceiver Architecture (Mar. 19, 2009).